Regulation of Autophosphorylation Controls PLK4 Self-Destruction and Centriole Number

Polo-like kinase 4 (PLK4) is a major player in centriole biogenesis: in its absence centrioles fail to form, while in excess leads to centriole amplification [1-5]. The SCF-Slimb/beta TrCP-E3 ubiquitin ligase controls PLK4 levels through recognition of a conserved phosphodegron [6-13]. SCF-Slimb/beta TrCP substrate binding and targeting for degradation is normally regulated by phosphorylation cascades, controlling complex processes, such as circadian clocks and morphogenesis [14]. Here, we show that PLK4 is a suicide kinase, autophosphorylating in residues that are critical for SCF-Slimb/beta TrCP binding. We demonstrate a multisite trans-autophosphorylation mechanism, likely to ensure that both a threshold of PLK4 concentration is attained and a sequence of events is observed before PLK4 can autodestruct. First, we show that PLK4 trans-autophosphorylates other PLK4 molecules on both Ser293 and Thr297 within the degron and that these residues contribute differently for PLK4 degradation, the first being critical and the second maximizing auto-destruction. Second, PLK4 trans-autophosphorylates a phospho-cluster outside the degron, which regulates Thr297 phosphorylation, PLK4 degradation, and centriole number. Finally, we show the importance of PLK4-Slimb/beta TrCP regulation as it operates in both soma and germline. As beta TrCP, PLK4, and centriole number are deregulated in several cancers [14-17], our work provides novel links between centriole number control and tumorigenesis.